This study proposes to identify one of the genes responsible for a form of preaxial polydactyly that can be inherited as an autosomal dominant trait. Preaxial polydactyly refers to an excess of digits on the thumb side of the limb. A large six-generation family was identified in which 20 individuals have preaxial polydactyly. Blood samples were obtained from multiple individuals in the family and the DNA was extracted for genetic studies. Subsequent genetic mapping demonstrated that the gene responsible for this form of polydactyly resides on the long arm of chromosome 7. The goal of this proposal is to determine the precise location of the gene from preaxial polydactyly and to study the structure and expression of the gene once identified.